The invention relates to an electrical circuit for controlling the operation of the relay of a fuel pump depending upon the number of revolutions of the motor supplied by the fuel pump.
The electrical circuit of the invention cuts off the fuel supply of a monitored motor, if a permissible maximum number of revolutions is exceeded. The invention is particularly adapted for use with automotive vehicles, however, it can be used with other monitored motors as well.
In accordance with the invention, an electrical circuit is provided which controls the operation of a relay that controls the operation of the fuel pump, and pulses analogous to the number of revolutions of the monitored motor are coupled to the electrical circuit. Those pulses are compared with a specified fixed comparison value which corresponds to the minimally permissible time between two ignition pulses. When the monitored motor is running, opening of the fuel pump relay circuit takes place only if the minimally permissible time between the ignition pulses falls short; and closing again takes place only in case of an at least slightly greater time interval between two ignition pulses.
A feature of the invention is that there is provided, in series with the fuel pump relay, the collector-emitter path of a transistor whose base is controlled by the output of a flip-flop. This flip-flop, in turn, has coupled to it both timing pulses from a pulse generator TD and the output of a Schmitt trigger, with the Schmitt trigger generating a constant signal at its output which corresponds to the smallest permissible pulse interval between two ignition pulses. The Schmitt trigger is set by the negative edge of each ignition pulse and remains for a fixed time. The output of the flip-flop is a "1" signal, as long as its input from the Schmitt trigger is a "1" signal and its input from the pulse generator is a "0" signal. The "1" signal from the flip-flop maintains the transistor conductive, and with the transistor conductive, the fuel pump relay is operated to energize the fuel pump. The output of the flip-flop is a "0" signal if both of its inputs are a "1" signal, and the transistor is rendered non-conductive cutting off the fuel pump relay and hence the fuel pump.
A further feature is the provision of another transistor which inverts by 180.degree. the arriving ignition signal. The ignition signal normally has a relatively flat leading positive edge and a relatively steep-slope trailing negative edge, thus a second steep-slope leading edge is produced, since the previously negative steep-slope edge forms then a positive steep-slope edge. Moreover, the transistor blocks with a negative signal and thereby protects the following electronic system.
A still further and preferred feature is the fact that the frequency of the timing pulses from the pulse generator is halved by a flip-flop, and that the determination as to whether the permissible number of revolutions or interval between two timing pulses has been exceeded is carried out edge-controlled at the flip-flop.
Furthermore, the transistor which inverts the arriving ignition signal couples the inverted signal to the flip-flop, and the inverted output Q of the flip-flop is coupled back to its input. The Q output of the flip-flop controls both the input of another flip-flop and, by way of a capacitor which is a component of a differentiating element, controls the input of a Schmitt trigger whose discharging transistor controls the charging of the capacitor of a clock element. The halving of the pulse sequence by the flip-flop prevents the next ignition pulse from falling in the discharging phase or the capacitor of the clock element. By means of this circuit there is recognized that when the Q output of the first flip-flop is coupled to the other flip-flop, and the output of the Schmitt trigger is positive, the maximally permissible number of revolutions is exceeded.
Furthermore, it is advantageous that the minimally permissible interval between two pulses is formed by a monostable trigger stage with its clock element.
Moreover, there is intended that the determination takes place always after each second timing pulse on the pulse generator. Beyond that, it is advantageous that by a change of the clock element the circuit is usable for all motor types.
Still another feature is that between the output of the Schmitt trigger and the input of the flip-flop there is connected by way of a base series resistance the base of a transistor whose emitter is grounded and whose collector is put on operating voltage either by way of a resistor and a capacitor in series with it, or by way of resistor which is in parallel with the series connected resistor and capacitor. A connection between the capacitor and resistor which are in series is made to the setting input of the flip-flop. With motor speeds of &gt;0 to .ltoreq.100 r/min., the arrangement is operative to couple a "0" signal potential to the setting input of the flip-flop, so that its dynamic inputs are effective. Furthermore, with this arrangement, the after-running time of the fuel pump (usually less than 1 s) is regulated after the ignition has been turned off. Also, the normalization of the flip-flop takes place by this arrangement.
Moreover, it is advantageous that the Q output of the flip-flop is coupled back to the input of the Schmitt trigger with interposition of a diode and of a resistor in series with it, to produce a hysteresis which is adjustable and can amount, for instance, to 100 rev/min. during which, after the fuel pump is turned off, the fuel pump cannot be turned on because the number of revolutions is too high. The transistor T3 is rendered conductive again, only if the maximum number of revolutions falls short by, for instance, 100 rev/min. Without hysteresis, the operation would be nearly continuous in connection with a maximum number of revolutions because constant turning on and turning off of the fuel pump would take place. However, the electrical circuit is functionally efficient also without hysteresis.
Still another feature consists in the fact that, by way of a decoupling diode and a base resistor, the base of the transistor can be put on a terminal on battery voltage over the ignition lock.
Accordingly, it is an object of the invention to provide an arrangement or electrical circuit for actuating the relay of a fuel pump depending upon the number of revolutions of the motor supplied by the fuel pump.